This add-on solves the problem of "alt-text" in Mastodon's web client being unselectable, uncopyable, and only visible via a tooltip. It places a box at the top of the screen when images or videos (i.e. in a post's gallery) are expanded, displaying the alt text of the current image or video.
The box is transparent by default, only showing a single line of alt text, but it gains a background and expands when hovered with your mouse. In case the alt text is too long to fit onto your screen, the box becomes scrollable. The text can be copied by selecting it as desired.
